Polymerization of vinylcarbazole on copper(II)-13X molecular sieves: Role of copper(II) salts

Copper(II)-exchanged-13X molecular sieves, prepared from four copper(II) salts, namely, sulfate, nitrate, chloride, and acetate, and their activities in the polymerization of N-vinylcarbazole at a fixed copper ion exchange level were studied. From the kinetic characteristics of polymerization it was established that the variation in activities of the Cu-exchanged sieves is due primarily to the difference in the pH of the original salt solution, which is responsible for the varying degree of proton exchange with the zeolite during copper ion exchange. A first-order dependence of the rate of polymerization was observed with respect to H⁺ ion concentration of the original copper-salt solution. It was further established that the rate of polymerization of exchanged copper ion, at a hypothetical zero proton concentration, is low. A mechanism of polymerization of NVC on copper-exchanged-13X zeolite was suggested on the basis of the results obtained.     

Highly efficient water promoted allylation and propargylation of arylepoxides via rearrangement-carbonyl addition

A simple and highly efficient one-pot procedure for allylation and propargylation of arylepoxides has been developed. A combination of SnCl₂ and catalytic Pd(0) or Pd(II) promotes the reaction of organic halides and epoxides in DMSO with controlled water addition, leading to the regioselective formation of the corresponding homoallyl and homopropargyl alcohols in good yields.     

Production of Bioactive Compounds with Broad Spectrum Bactericidal Action,Bio-Film Inhibition and Antilarval Potential by the Secondary Metabolites of the Endophytic Fungus Cochliobolus sp. APS1 Isolated from the Indian Medicinal Herb Andrographis paniculata

Endophytes, being the co-evolution partners of green host plants, are factories of pharmaceutically valuable novel natural products. Cochliobolus sp. APS1, an endophyte of Andrographis paniculata (Green Chiretta), produces a plethora of natural bioactive compounds and the multipotent alkaloid Aziridine, 1-(2-aminoethyl)-, is the prime one among them. The isolate exhibited antibacterial, anti-biofilm, and antilarval potency. The MIC and MBC values of the ethyl-acetate culture extract ranged from 15.62 to 250 µg/mL against ten pathogenic microorganisms (including MRSA and VRSA). Killing kinetics data along with the leakage of macromolecules into the extracellular environment supports the cidal activity of the antibacterial principles. The broad spectrum antibacterial activity of Aziridine, 1-(2-aminoethyl)-, was optimized by a one-variable-at-a-time system coupled with response surface methodology, which led to a 45% enhancement of the antibacterial activity. The maximum response (22.81 ± 0.16 mm of zone of inhibition against MRSA) was marked in 250 mL Erlenmeyer flask containing 90 mL potato dextrose broth supplemented with (g%/L) glucose, 9.7; urea concentration, 0.74; with medium pH 6.48; after 8.76 days of incubation at 26 °C. APS1 strongly inhibited biofilm formation in the tested pathogenic microorganisms and acts as a larvicidal agent against the Dengue-vector Aedes aegypti. This is probably the first report of Aziridine, 1-(2-aminoethyl)-, from any endophytic source. Cochliobolus sp. APS1 possesses industrial importance for the production of bioactive alkaloids.     

Characteristics of electrochemically grown dendritic metallic zinc

A simple electrochemical process has been implemented to fabricated fractal structured leaf-like metallic zinc. The fabricated material was structurally characterized using X-ray diffraction that reveals the hexagonal unit cell structure. Also the growth of the structure is anisotropic. Field emission scanning electron microscopic images revealed clearly the leaf-like morphology of the fabricated material is fern like and ∼500 μm in length, ∼50-60 μm wide and the platelets thickness is ∼5 μm. The growth of this structure is diffusion controlled and locally accomplished with the oriented attachment. Raman shift measurement revealed the existence of surface optical phonon modes which is very significant for surface defects.     

A theoretical study of antioxidant activity of some Schiff bases derived from biologically important phenolic aldehydes and phenylenediamines

Because of their numerous biological as well as industrial importance, the study of Schiff bases is an emerging field for the researchers, in recent time. In this study, we have designed some Schiff bases derived from biologically important precursors. The antioxidant activities of the designed compounds are thoroughly studied theoretically using density functional theory taking various parameters like bond dissociation enthalpy, ionization enthalpy, proton dissociation enthalpy, and electron transfer enthalpy followed by the study of effects of solvent, spin density, and molecular orbital on antioxidant activity of the compounds. The comparison of antioxidant activity of the compounds with that of phenol and their parent aldehydes reveals the superior antioxidant activity of the designed compounds. This study contributes towards the information of an important bridge between bioorganic and computational chemistry.     

Controlled Markov processes on the infinite planning horizon: Weighted and overtaking cost criteria

Stochastic control problems for controlled Markov processes models with an infinite planning horizon are considered, under some non-standard cost criteria. The classical discounted and average cost criteria can be viewed as complementary, in the sense that the former captures the short-time and the latter the long-time performance of the system. Thus, we study a cost criterion obtained as weighted combinations of these criteria, extending to a general state and control space framework several recent results by Feinberg and Shwartz, and by Krass et al. In addition, a functional characterization is given for overtaking optimal policies, for problems with countable state spaces and compact control spaces; our approach is based on qualitative properties of the optimality equation for problems with an average cost criterion.Research partially supported by the Engineering Foundation under grant RI-A-93-10, in part by the National Science Foundation under grant NSF-INT 9201430, and in part by a grant from the AT&T Foundation.Research partially supported by the Air Force Office of Scientific Research under Grant F49620-92-J-0045, and in part by the National Science Foundation under Grant CDR-8803012.     

A zero sum differential game in a Hilbert space

We study a zero sum differential game of fixed duration in a separable Hilbert space. We prove a minimax principle and establish the equivalence between the dynamic programming principle and the existence of a saddle point equilibrium. We also prove sufficient conditions for optimality.     

Understanding the role of surfactants on the preparation of ZnS nanocrystals

We have synthesized surface modified ZnS nanoparticles of size 2-3 nm using non-ionic surfactant-stabilized reverse emulsions. The non-ionic surfactants in the Span series, i.e. sorbitan monolaurate (Span 20) and sorbitan monooleate (Span 80) of hydrophilic-lipophilic balance (HLB) values of 8.6 and 4.3, respectively, have been used for the stabilization of emulsions. The role of these surfactants in controlling the size and properties of the ZnS nanoparticles has been discussed. The triethylamine (TEA) has been proved to be the effective surface modifying (capping) agent for the preparation of free-standing ZnS nanoparticles. The Span 20 with the higher HLB value of 8.6 has been found to be highly suitable in synthesizing TEA-capped ZnS nanoparticles of smaller size and higher photophysical characteristics compared to that of the Span 80 of lower HLB value of 4.3. A mechanism for the formation of TEA-capped ZnS nanoparticles from the surfactant-stabilized reverse emulsions has been proposed.     

In search of oligo(2-thienyl)-substituted pyridine derivatives: a modular approach to di-, tri- and tetra(2-thienyl)pyridines

Herein, we describe our attempts to systematically prepare a series of oligo(2-thienyl)-substituted pyridine derivatives. The crucial starting material, a β-alkoxy-β-ketoenamide, is easily available on a large scale by the reaction of lithiated methoxyallene with thiophene-2-carbonitrile and thiophene-2-carboxylic acid. This three-component reaction is followed by intramolecular cyclization to yield the suitably functionalized 2,6-di(2-thienyl)-substituted pyridine derivates. The two oxygen atoms allow the programmed activation of positions C-3, C-4, or C-5 of the pyridine ring to perform palladium-catalyzed coupling reactions with thiophene-2-boronic acid or 2-(tributylstannyl)thiophene, and alternatively, reductive removal of groups. With this concept, we were able to prepare five pyridine derivatives with 2-thienyl substituents in the 2,6-, 2,3,6-, 2,4,6-, 2,3,4,6-, and 2,3,5,6-positions. 2,3,4,5,6-Penta(2-thienyl)pyridine was not available with our methods. The UV/Vis and fluorescence spectra of all pyridines were recorded and showed a dependence on the substitution pattern and protonation state. For the protonated 2,3,5,6-tetra(2-thienyl)-substituted pyridine, a Stokes shift of about 180 nm with an emission at 515 nm was observed.